The biotechnological production of substances of interest is, on an industrial scale, generally performed by cultivating a microorganism in a liquid medium, wherein said microorganism is capable of producing said substance of interest under the cultivation conditions. During such liquid fermentation, individual microorganism cells experience conditions that vary greatly and in a complex way over time. In response to such changing conditions, microorganism cells may respond by altering gene expression, which in turn may lead to an undesirably low production of the substance of interest. There is correspondingly a need to provide microorganisms with improved resilience against unfavourable fermentation conditions, thus allowing for an increased production of a substance of interest compared to comparable microorganisms.
It has thus frequently been tried to determine stress conditions during fermentations and to modify the genetic makeup of microorganisms in order to improve their resilience against such stress conditions. Unfortunately, analysis of fermentation conditions experienced by individual microorganism cells and their genetic reactions to such conditions is notoriously difficult. Wiegand et al. (Fermentation stage-dependent adaptations of Bacillus licheniformis during enzyme production; Microbial Cell Factories 2013, 12:120) have tried such analysis. However, understanding of fermentation conditions still remains largely incomplete.
While Wiegand et al. reported that no vegetative catalase (KatA) protein accumulation over time could be observed in Bacillus licheniformis during liquid fermentation production of a subtilisin protease, the inventors have surprisingly found that increased catalase activity improves overall fermentation characteristics e.g. of B. licheniformis in the liquid fermentation production of e.g. proteases. This was even more surprising as, according to Wiegand et al., O2 partial pressure (pO2) is severely reduced throughout basically all stages of such fermentation. Thus, formation of hydrogen peroxide as a major stressor was not to be expected.
It was thus an object of the present invention to provide materials and methods for improving fermentations, for reducing oxidative stress during fermentations, for removing hydrogen peroxide from a medium, for increasing hydrogen peroxide tolerance of a microorganism and/or for protecting a microbially produced substance against oxidation. It was also an object of the present invention to provide a suitable catalase for the aforementioned goals, and to provide microorganisms making use of such catalase, and to provide corresponding fermentation methods.